Unauthorized use of proprietary computer programs is widespread. Since development costs of most software are substantial, it is necessary for developers of such software to set licensing fees for the use of such software at a sufficient level to recover such costs and to provide a profit to the developers. Such pricing provides an incentive for some users to attempt to obtain programs at lower costs by unauthorized copying or by using on several sites software which has been licensed for only one site.
Various methods have been employed for preventing the use of programs by persons who have obtained them in an unauthorized manner. Such methods include the use of a hardware "key" which must be used with the program, the encryption of programs, and the use of "trap" conditions.